An unstable processing solution may be created when processing ingredients, for example a developer fluid and an activator, are mixed together. The unstable processing solution will have a tendency to deteriorate over a short period of time, thus a relatively small amount of exposed photosensitive material can be processed before the unstable solution would have to be discarded.
A new processing solution would have to be created each time the unstable processing solution is discarded. This can be time consuming for the operator of the processing apparatus.